Field of the Invention
The present invention relates to an internal combustion engine.
Description of the Related Art
Some improvements of an internal combustion engine, such as maximization of the opening areas of an intake valve and an exhaust valve or optimization of the opening positions, have been proposed to improve the intake efficiency from an intake port and the scavenging efficiency to an exhaust port. In the operating state of the internal combustion engine, there may be an overlap period when the valve-opening of the intake valve overlaps with the valve-opening of the exhaust valve. In this overlap period, a blow-by phenomenon is likely to occur, in which the fresh air or air-fuel mixture flowing from the intake port into a combustion chamber directly flows out to the exhaust port. The blow-by phenomenon causes problems such as deterioration of the emission performance of the internal combustion engine and reduction of the power of the internal combustion engine.
According to a technique disclosed in Patent Literature 1, a protruded wall that is protruded toward a combustion chamber is provided along an intake port-side peripheral edge at an opening of an exhaust port. The protruding height of the protruded wall is set to be smaller than a predetermined amount, and a clearance between the protruded wall and a bevel portion of an exhaust valve is set to be smaller than the protruding height of the protruded wall. This proposed configuration aims to suppress the blow-by phenomenon and suppress reduction of the scavenging efficiency by the protruded wall. Patent Literature 2 also discloses a technique that a protruded wall that is protruded toward a combustion chamber is provided along an intake port-side peripheral edge at an opening of an exhaust port. This protruded wall, however, serves as a guide wall to acceleration formation of a swirl flow in the combustion chamber and does not aim to suppress the blow-by phenomenon.